The application of molluscicides to the breeding-places of Australorbis glabratus-the intermediate host of Schistosoma mansoni in Venezuela-is discussed, with special reference to the equipment required and the techniques employed. The characteristics of the three molluscicides in use-copper sulfate, sodium pentachlorophenate, and copper pentachlorophenate-are outlined, and the treatment both of running waters (irrigation canals and streams) and of still waters (ponds and marshes) is described in detail.